1. Field of the Invention
The present invention relates to a discharging lamp lighting apparatus for a high pressure mercury-arc lamp, a metal halide lamp or the like.
2. Description of the Prior Art
In recent years, security and an environmental protection performance of a vehicle has been desired, and individuality of the vehicle has also been important. Desires for improved travelling security and vehicle body design have required, with respect to a head light, an increase in an amount of light and small-sized design. However, in a conventional electric lamp for the vehicle, it has already been difficult to meet such requirements. Hence, adoption of a discharging lamp as a new light source of vehicles is studied.
FIG. 24 is a general view showing a structure of 35 W metal halide lamp which is one kind of discharging lamp 12. In the metal halide lamp, a silica tube 121 is sealed at both ends thereof, and an arc tube 122 is disposed at an intermediate portion of the silica tube 121. The arc tube 122 has tungsten electrodes 123a, 123b opposed to each other, and the tungsten electrodes 123a and 123b are connected to external leads 125a, 125b through molybdenum foils 124a, 124b. Further, the arc tube 122 is filled with a metallic halide 126 obtained by combining several different metals such as sodium and scandium with iodine, a starting gas (for example, a xenon gas) 127, and mercury 128.
The discharging lamp 12 as described above is significantly different from the conventional electric lamp in that the conventional electric lamp can emit by simply applying voltage to one filament while the discharging lamp uses an arc generated between the electrodes as an emitter and requires a lighting apparatus to control the arc light.
A description will now be given of a part which the lighting apparatus should play by illustrating an emission mechanism of the discharging lamp. The discharging lamp 12 requires high voltage ranging from several kilovolts less than ten to over ten but less than twenty kilovolts for an initial period. Thus, the lighting apparatus generates high voltage to apply the voltage between the tungsten electrodes 123a and 123b of the discharging lamp 12. Discharge is thereby started between the tungsten electrodes 123a and 123b, resulting in a current flow between the tungsten electrodes 123a and 123b. Thereafter, the lighting apparatus supplies the maximum rated power or current of the discharging lamp 12 so as to increase an amount of light emitted from the discharging lamp 12 as soon as possible. At this time, the flowing current activates the starting gas 127 filled in the discharging lamp 12 to start arc discharge of the starting gas 127.
Further, discharging lamp voltage of the discharging lamp 12 at this time increases from about 20 V, and the lighting apparatus adjusts to gradually decrease power fed to the discharging lamp 12 according to the voltage so as to adjust the amount of light emitted from the discharging lamp 12 in an overload state. At a time of control of the feeding power, a temperature in the discharging lamp 12 rapidly increases to vaporize the mercury 128, thereby starting arc discharge of a mercury gas. A temperature at a center portion of the mercury arc reaches about 4500K (Kelvins), and a higher temperature and higher pressure are generated in the arc tube 122. Accordingly, evaporation of the metallic halide 126 is started so that a metallic ion is separated from a halogen ion in the arc, resulting in emission of the metallic ion with spectrum inherent in metals.
After almost the entire metallic halide 126 is vaporized, the arc light has a final form and reaches final output, and the discharging lamp voltage of the discharging lamp 12 is saturated, resulting in stable voltage (hereinafter referred to as final discharging lamp voltage). At the time, the lighting apparatus fixes power supplied to the discharging lamp 12 to rated power so that the discharging lamp 12 can emit stable light without flickering.
Such a discharging lamp lighting apparatus is disclosed in, for example, Japanese Patent Application Nos. 4-129365 and 4-276791 which have previously been filed by the applicant.
FIG. 25 is a circuit diagram of the conventional discharging lamp lighting apparatus.
In FIG. 25, reference numeral 1 is a battery power source, and 13 is an inverter circuit connected to the battery power source 1 through a lighting switch 2. The inverter circuit 13 includes switching devices 13a, 13b which are alternately turned ON and OFF, a boosting transformer 13c for boosting voltage of the battery power source 1 converted into ac current by the switching devices 13a and 13b to desired voltage, and a coupling capacitor 13d.
Reference numeral 14 is a drive section, and 15 is an LC series resonance circuit including a choke coil 15a, capacitors 15b and 15c, a resistor 15d, and a switch 18. In this case, in order to avoid reduction of sharpness Q of resonance, a value of resistance in the resistor 15d is defined as a negligible value as compared to effective resistance due to the choke coil 15a and the capacitors 15b, 15c in resonance. Reference numeral 12 is the discharging lamp, 16 is a self-excited oscillation circuit serving as original oscillation for outputting resonance frequency, and 17 is a TTL level converting circuit.
Reference numeral 6 is voltage detecting means for detecting the voltage of the discharging lamp 12 after dielectric breakdown from a node between the capacitors 15b and 15c through the switch 18, 5 is current detecting means for detecting current in the discharging lamp 12 through a current transformer 19, and 9 is a dielectric breakdown detecting circuit to detect rush current flowing in the discharging lamp 12 during the dielectric breakdown through the current transformer 19 so as to transmit a signal indicating whether or not the dielectric breakdown occurs.
Reference numeral 70 is control means including a microcomputer or the like, for instructing ON-OFF operations of the switch 18 and for controlling frequency outputted to the inverter circuit 13 depending upon signals transmitted from the voltage detecting means 6, the current detecting means 5, and the dielectric breakdown detecting circuit 9. There is provided another means for storing the final discharging lamp voltage depending upon a signal transmitted from the voltage detecting means 6. FIG. 26 is a diagram showing a detailed periphery of the discharging lamp 12. In FIG. 26, reference numeral 21 is a discharging lamp exchange detecting switch which is automatically turned ON when the discharging lamp 12 is removed, 22 is a fix base for fixing the discharging lamp 12 including a socket, and 23 is the socket for fixing the discharging lamp.
In the apparatus, when a light switch 2 is turned ON to control flash of the discharging lamp 12, the control means 70 opens the switch 18 so as to open input from the voltage detecting means 6, and is in a waiting state until the control means 70 receives a signal from the dielectric breakdown detecting circuit 9.
On the other hand, the self-excited oscillation circuit 16 is operated to output a self-excited oscillation frequency. The oscillation frequency is resonated in the inverter circuit 13, the LC series resonance circuit 15, and the TTL level converting circuit 17. Subsequently, amplified high voltage is applied to the discharging lamp 12 to cause the dielectric breakdown between the electrodes in the discharging lamp 12. At the moment, the discharging lamp 12 is in a substantially short-circuited state so that the rush current flows in the discharging lamp 12. The rush current is detected by the dielectric breakdown detecting circuit 9 via the current transformer, and the detected signal is transmitted to the control means 70 so as to decide that the dielectric breakdown occurs.
The control means 70 receives the signal from the dielectric breakdown detecting circuit 9 to stop output from the self-excited oscillation circuit 16 to the inverter circuit 13. Instead, the control means 70 outputs a frequency to conduct rated current (ranging from 2 to 3 A) as a normal lighting signal to the inverter circuit 13 via the drive section 14. Concurrently, the control means 70 closes the switch 18 to connect an input terminal of the voltage detecting means 6 with the node between the capacitors 15b and 15c.
Subsequently, the discharging lamp 12 is turned ON by flowing current based upon the frequency to conduct the rated current (ranging from 2 to 3 A) outputted into the inverter circuit 13 via the drive section 14. Here, the current flowing in the discharging lamp 12 is compared with a predetermined value in the current detecting means 5 so as to determine whether or not the discharging lamp 12 is turned ON. If it is determined that the discharging lamp 12 is not turned ON, the above operation is repeated. Otherwise, the voltage detecting means 6 reads the voltage of the discharging lamp 12.
In this case, if the final discharging lamp voltage V is not stored in storing means of the control means 70, the final discharging lamp voltage V.sub.x is defined as the minimum rated voltage in specification of the discharging lamp 12 to set a power control pattern (for example, a pattern which is smoothly attenuated in a range from 75 to 35 W). A target current can be calculated depending upon the power and the voltage of the discharging lamp 12 detected from the voltage detecting means 6 by an expression: current=power/voltage. The frequency outputted from the control means 70 is reduced if the current flowing in the discharging lamp is smaller than the target current, and the frequency is increased if the current is larger than the target current. It is thereby possible to cause the discharging lamp voltage to come closer to the final discharging lamp voltage V.sub.x according to the smooth attenuation pattern. The frequency is varied and adjusted so as to maintain rated power (of, for example, 35 W) when the discharging lamp voltage becomes equal to or more than the final discharging lamp voltage V.sub.x, resulting in performing lighting control.
Otherwise, if the final discharging lamp voltage V.sub.x is stored, the minimum rated voltage in the specification in the above control is replaced with the stored value, and the power control pattern is also varied to another pattern corresponding to new final discharging lamp voltage V.sub.x. Similar lighting control is performed so as to provide power suitable for the discharging lamp voltage at this time.
The lighting control is performed as set forth above, and thereafter the lighting switch 2 is turned OFF. Then, after it is confirmed that the discharging lamp 12 is in a stable state, final discharging lamp voltage V.sub.x at that time is stored by the voltage detecting means 6 in a memory in the control means 70. Any desired time period up to a discharging lamp stable state which is experimentally defined in advance is set to decide whether or not the time period has elapsed, thereby confirming the stable state of the discharging lamp 12. It is thereby possible to prevent from storing erroneous final discharging lamp voltage V.sub.x even if the lighting switch 2 is turned OFF before the discharging lamp stable state.
The final discharging lamp voltage V.sub.x is stored for each lighting. It is thereby possible to, even if the final discharging lamp voltage V.sub.x is varied due to degradation of the discharging lamp or the like, perform the optimal lighting control in the state. In this case, the voltage detecting means 6 and the current detecting means 5 have desired sampling times.
When the discharging lamp 12 is removed, the discharging lamp exchange detecting switch 21 is turned ON, and a high level signal is inputted into the control means 70. The signal erases the final discharging lamp voltage V.sub.x stored in the control means 70. At the next lighting time, it is decided that the final discharging lamp voltage V.sub.x is not stored, and lighting control corresponding to the minimum rated voltage value is performed.
The discharging lamp lighting apparatus as described in detail above is provided with the means for storing the final discharging lamp voltage V.sub.x. Thus, the lighting control can be performed by the power control pattern corresponding to the final discharging lamp voltage V.sub.x for each discharging lamp. It is thereby possible to provide the stable state more rapidly, and optimize a rise characteristic of the amount of light. Further, when the final discharging lamp voltage V.sub.x is stored, it is decided before the storing whether or not the discharging lamp 12 is in the stable state. It is thereby possible to avoid lighting control based upon erroneous final discharging lamp voltage V.sub.x. In addition, the minimum rated voltage is provided to prevent the amount of light of the discharging lamp in the stable state from exceeding an amount of light at a time of the rated power, and to avoid reduction of a lifetime.
The conventional discharging lamp lighting apparatus, however, is provided as set forth above so that the following problems are generated. No final discharging lamp voltage V.sub.x is stored at an initial lighting time or at an initial lighting time after exchanging the discharging lamp. Hence, the power control is performed by using the minimum rated voltage of the discharging lamp in the specification as the control target voltage, and a rise of the amount of light becomes slower than that in case of the optimal control. Further, when the erroneous final discharging lamp voltage V.sub.x is stored due to noise and so forth, the optimal control can not be performed at the next lighting time. Thus, the rise characteristic of the amount of light is deteriorated and the lifetime is reduced. In addition, it is necessary to provide means for detecting whether or not the discharging lamp is exchanged, resulting in an expensive apparatus.